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Catalyst design for low temperature oxidation of methane to methanol

Williams, Christopher Paul 2018. Catalyst design for low temperature oxidation of methane to methanol. PhD Thesis, Cardiff University.
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Abstract

Abundantly available through natural gas, methane is largely underutilised as a resource. Furthermore, providing a potential alternative to the production of valuable petrochemicals, direct valorisation of methane would prolong reserves of feedstock petrochemicals derived from dwindling crude oil. Instead, due to lack of on-site valorisation processes, methane is largely flared during the production of crude oil. Even so, industrial application of used methane involves an indirect and energy intensive route transforming methane to synthesis gas (CO2 and H2). Further processing is then applied to effectively valorise to the desired liquid petrochemicals. Alternatively, a direct on-site route to methanol under mild conditions would limit the environmental impact of an energy intense indirect process. In addition, methanol provides a valuable non-crude oil source as an intermediate to a vast number of applications across several industries. One avenue investigated, effectively utilised AuPd/TiO2 catalyst for the oxidation of methane using H2O2 at low temperature (50 °C). Inspiring the first section of this thesis, the synthesis of AuPd/TiO2 by impregnation provides poor control yielding a broad range of nanoparticle sizes with poor control of nanoparticle composition. Therefore, the first chapter investigates the influence of AuPd particle size, selecting sol immobilisation for controlled preparation of starting material with narrow size distribution. The application of heat treatment to promote particle size increases was investigated to confirm an influence for methane oxidation. During this work, further influences were observed during initial testing and were evaluated to improve understanding and increase catalyst productivity. These influences included variation in AuPd nanoparticle size, TiO2 support phase and surface area changes. Producing variables which directly allowed controlled utilisation of H2O2 then provided avenues to produce a significantly improved catalyst, requiring lower metal loading (0.13 wt.%) with higher productivity and H2O2 efficiency. The second section of this thesis investigates the application of perfluorinated solvent for the selective oxidation of methane. Although proposed to be environmentally benign, the application of pre-formed H2O2 requires its production via the anthraquinone process. Instead, the direct incorporation of molecular oxygen is considered the goal for catalytic oxidation processes. Offering higher gas solubilities for both methane and oxygen, a perfluorinated solvent was applied for investigations into use of molecular oxygen for methane oxidation. The development of biphasic system trialled the application of radical initiators but found activity independent of catalyst. Instead, the in-situ generation of H2O2 from H2 and O2 was investigated.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 24 May 2019
Last Modified: 24 May 2019 11:52
URI: http://orca-mwe.cf.ac.uk/id/eprint/122839

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